A device for forming a layer of fibrous material of homogeneous structure

ABSTRACT

In the device, provision is made for an electrostatic neutralizer for charged fibres, said neutralizer being installed at the inlet of a wind tunnel, whereas a slit-type jet nozzle is installed at the place where a serrated drum ajoins the wind tunnel, said nozzle extending along the entire length of the drum to deliver air to the zone of fibres removal from the serrated drum.

United States Patent 1 Guschin Dec. 4, 1973 DEVICE FOR FORMING A LAYER OF FIBROUS MATERIAL OF HOMOGENEOUS STRUCTURE [76] Inventor: Alexandr Evgenievich Guschin,

Kovensky prospekt 13, Leningrad, U.S.S.R.

22 Filed: Sept. 27, 1972 21 Appl. No.: 292,829

[52] US. Cl. 317/262 R, 317/2 R, 264/121 [51] Int. Cl. B29j 1/00, H05f 3/06 [58] Field of Search 264/121; 317/2 R,

[56] References Cited UNITED STATES PATENTS 2,577,205 12/1951 Meyer et a1 264/121 2,635,301 4/1953 Schubert et a1 264/121 2,646,381 7/1953 Duvall 264/121 2,886,484 5/1959 French et al.... 264/121 3,453,355 7/1969 Rudloff 264/121 3,691,009 9/1972 Opderbeck et a]. 264/121 3,544,414 12/ 1 970 Simison 264/121 Primary Examiner-L. T. l-lix Attorney-John C. Holman et a1.

57 ABSTRACT In the device, provision is made for an electrostatic neutralizer for charged fibres, said neutralizer being installed at the inlet of a wind tunnel, whereas a slittype jet nozzle is installed at the place where a serrated drum ajoins the wind tunnel, said nozzle extending along the entire length of the drum to deliver air to the zone of fibres removal from the-serrated drum.

2 Claims, 2 Drawing Figures PATENTEDUEE m 3 777 231 SHEET 1 [IF 2 PATENTEDUEC 4191s SHEET 2 [1F 2 DEVICE FOR FORMING A LAYER OF FIBROUS MATERIAL OF HOMOGENEOUS STRUCTURE This invention relates to devices for forming a layer of fibrous material of homogeneous structure and can be utilized in pulp-and paper, textile, and constructionmaterial industries for producing various kinds of paper, non-woven fabric, construction boards, felt.

Implied under a layer of fibrous material of homogenous structure is such a layer in which the density of fibre mass comprised in each unit volume of alayer of fibrous material is constant or varies insignificantly.

A degree of structural homogeneity can be determined indirectly by optical method with the help of a The variation factor for a layer of fibrousmaterial of homogeneous structure (as determined by the above mentioned technique) is valued as 10-30 percent.

The need for producing a layer of fibrous material homogeneous in structure is dictated by the fact the structure homogeneity of a layer of fibrous material makes it possible to obtain a fibrous material uniform by its mechanical-and-physical characteristics.

For example, when producing a filtering fibrous material the structural homogeneity of a layer of fibrous material decides the degree of uniformity of such mechanical-and-physical characteristics of the filtering material as porosity, tear resistance, resistance to snicking, rate of stretching, i.e., the structural homogeneity of a layer of fibrous material bears effect onthe quality of the product.

The present invention is applicable in various machines, plants, production lines, wherein a homogeneous fibrous layer is to be obtained through a single stage production process.

To obtain a layer of fibrous material of homogeneous structure, use is made of fibres of different origin such as natural, chemical, inorganic of 2-40 mm length. For example, in producing various kinds of industrial papets or non-woven materials, use is made of cotton, flax, asbestos, viscose fibre, polyamide, polyolefin, glass, carbon and other kinds of fibres.

Generally, a kind of fibre is to be selected in accordance with the properties of a material to be produced on the base of the given fibre (paper, non-woven material, etc.). Thus, asbestos fibres are practicable'for producing a material possessing high thermal and electrical insulation properties, polypropylene fibrefor those resistant to alkalis at high temperature, cotton and lavsan" for biologically safe products, etc.

Application of fibrous materials with various properties as-exemplified above, in different fields of industry (aviation, electrical engineering, metallurgy) makes way for solving important engineering problems.

Known in the art are devices for obtaining a layr of fibrous material, comprising a serrated drum and a brushing roll positioned there above. Disposed adjacently to the serrated drum is a funnel to direct fibrous particles onto a screen drum or a flat screen. The serrated drum breaks up the fibrous material into singular fibres and groups of fibres. The brushing roll, when rotating, removes fibrous particles from the serrated drum and throws them through the funnel onto a conveyor which is actually a flat screen, whereon they are being superimposed with the help of an exhaust blower. This results in a layer of fibrous material of homogeneous structure formed on the screen. 1

A device of an improved design has been developed to obtain a layer of fibrous material of homogeneous structure, in which fibres are removed from the serrated drum by means of an air stream.

The device comprises a feed unit to deliver fibrous mass onto one or two rotatable serrated dru'ms conjugate to a tube (of the Venturi type). Adjacent to the tube is a screen drum or a fiat screen.

Fibrous material is brought to the zone of the serrated drum. The latter, when rotating, separates fibrous material into singular fibres and groups of fibrous. From the surface of the drum the fibrous material is removed by an air stream which is induced in the tube by the exhaust blower; air is being exhausted from under the screen drum and delivered in the zone of the serrated drum. Upon entering the tube, fibres are dispersing in the air stream and conveyed by air towards the screen drum, upon which they are settling randomwise to form a layer of fibrous material of homogeneous structure.

Also known in the art isa device for obtaining a layer of fibrous material of homogeneous structure, comprising a wind tunnel.

The device includes a serrated drum mounted on a baseframe. Disposed adjacently to the serrated drum is a vertical wing tunnel consisting of an effuser, a working portion, and two diffusers with a constant-area section provided there between.

Positioned inside the tunnel effuser, is a grate to equalize the air stream. Provided at the top of the working portion is a blading device to vary the air stream velocity field profile (cf., e.g., USSR Authors certificate No. 274,650, C]. '55fl 6).

Fibrous material is brought into the device in the form of a coarse fibrous layer (carfiet) obtained from a beater or any other machine. The carpet is fed to a rotatable serrated drum which with its serrations breaks up the carpet intosingular fibres and groups of fibres being delivered to the working portion of the wind tunnel, wherein they are separated from the drum by an air stream.

The air stream is induced in the wind tunnel by means of an exhaust blower connected to the bottom portion of the tunnel.

Upon leaving the serrated drum, fibres are gradually distributing due to the flow turbulence throughout the entire space of the air stream in the course of moving towards a screen positioned in the bottom portion of the wind tunnel.

In such a manner, by way of distributing singular fibres and groups of fibres in the air stream, the air-andfibre suspension is established. As a result of filtering the suspension, a layer of fibrous material with randomly disposed fibres is formed on the screen. The layer forming process can take place either on a fixed or on a moving screen.

Uniformity of the air stream in the wind tunnel is achieved due to positioning a grate in the effuser and a blading device in the working portion of the tunnel.

A fine-dispersed air-and-fibre suspension is needed so as to obtain a layer of fibrous material possessing a high degree of homogeneity. An obligatory prerequisite for attaining the above aim associates with adequate separation of the fibrous mass into fibres. This requires an air stream having but small-size whirls only. Such a kind of an air stream ensures separation of grouped fibres into singular fibres and smaller groups of fibres.

The known device for forming a layer of fibrous material of homogeneous structure fails to provide an air stream having small-size whirls.

Another cause of establishing an air-and-fibre suspension possessing an insufficient degree of dispersion associates with grouping of separate fibres due to the effect of Coulombs law. This occurs due to friction of fibres against drum serrations when fibres are given static charges of either polarity at the moment of breaking up the fibrous material. Oppositely charged fibres obey Coulombs law when interacting.

Grouping of separate fibres also takes place due to their precipitation onto the walls of the wing tunnel under the action of an electric charge resulting from polarization of the material of the tunnel walls by the effects of the composite electric field produced by the flow of static charged fibres.

It is commonly known, that for obtaining a layer of fibrous material of homogeneous structure, a low concentration of air-and-fibre suspension must be maintained, at which practically independent motion of separate fibres can be ensured. This condition for fibres in motion prevents them from grouping; the degree of dispersion in air-and-fibre suspension, which effects the homogeneity of a fibrous material layer, is not reduced.

A device embodied according to the present invention for obtaining a layer of fibrous material can provide the air-and-fibre suspension of low concentration only in case the air stream established in the working portion of the wing tunnel is imparted a high velocity actually higher than 150 m/s or due to a reduced production capacity of the device, because the concentration of fibrous material in the air stream can be varied through increasing or reducing the flow rate of air consumed or the amount of fibrous material fed per unit of time.

High pressure and high power blowers are needed to achieve a flow velocity in the wind tunnel above 150 m/s, which leads to increased power consumption.

The effect of separating grouped fibres in transfer of fibrous material from the serrated drum to the air stream due to counterflow of air in the drum appears insufficient for obtaining a highdispersion air-and-fibre suspension.

It is therefore an object of the present invention to provide a device for forming a layer of fibrous material of homogeneous structure, which will ensure obtaining a fibrous layer with high degree of homogeneity of fibrous mass to permit manufacturing of materials possessing high mechanical-and-physical properties.

These and other objects are achieved due to the provision of a device for forming a layer of fibrous material of homogeneous structure by way of precipitating fibrous particles onto the screen of the wind tunnel, said particles being contained in air-and-fibre suspension established as a result of introduction into an air stream of singular and grouped fibres obtained during breaking-up of fibrous mass by the serrated drum, wherein, according to the invention an electrostatic neutralizer for charged fibres is provided at the inlet of the wind tunnel, whereas a slit-type jet nozzle is installed at the place where the serrated drum ajoins the wind tunnel, said jet nozzle being extended underneath the drum and along the entire length thereof to deliver air to the zone of removing fibres from the serrated drum for separating grouped fibres and intensive mixing thereof.

The electrostatic neutralizer for charged fibres may be embodied as a three-dimensional grate simultaneously serving the purpose of equalizing the air stream.

The essence of the present invention is as follows.

Due to the provision of an electrostatic neutralizer for charged fibres which is installed at the inlet of the wind tunnel, and a slit-type jet nozzle underneath the drum for air delivery, a high degree of separation of grouped fibres is achieved. This stems from the following. The neutralizer installed at the inlet of the tunnel ionizes air delivered to the tunnel and interacting with static charged fibrous particles. Due to this interaction, electrostatic charges of fibres are neutrilized to prevent grouping of fibrous particles in accordance with Coulombs law.

Simultaneously and owing to the provision of the slittype jet nozzle, a turbulent air flow with small-size whirls is established underneath the serrated drum. This structure of the air stream permits intensive separation of grouped fibres with simultaneous neutralization of static charge.

The turbulent air flow with small-size whirls is established in the following way.

The slit-type jet nozzle provided underneath the serrated drum is so disposed that the air stream ejected through the jet nozzle is passing between the drum serrations. In this case the drum serrations serve the function of turbulating elements which are instrumental in establishing small-size whirls in the stream.

Owing to that, an intensive separation of grouped fibres is achieved which, as it has been stated above, is a necessary prerequisite for forming a layer of fibrous material with high degree of homogeneity.

A combination, according to the present invention, of the slit-type air jet nozzle interacting with the neutralization of electrostatic charge yields a novel effect, viz. an intensive separation of grouped fibres.

The electrostatic neutralizer for charged fibres which is installed at the inlet of the tunnel may take the form of parallel arranged corona-discharge ionizing tubes or a bank of such tubes.

To prevent distortion of the air stream due to the installed electrostatic neutralizer for charged fibres, the present invention provides for a neutralizer made as a three-dimensional grate which is capable equalizing the air stream.

The three-dimensional grate, as implied by the present invention, is one with elements thereof representing vertically disposed plates.

Further dilution of the air-and-fibre suspension which makes realizable a high degree of structural homogeneity in the layer of fibrous material is carried out as follows.

The jet nozzle installed underneath the serrated drum ejects a flat-shaped air stream which is saturated with fibres transferred from the drum serrations. As a result.

asituation is provided when in the working portion of the wind tunnel of the device forforming a layer of fibrous material of homogeneous structure, the flat air stream saturated with fibres is found, merging the air stream established inthe tunnel proper. Merging of the two above-mentioned flows is accompanied with an intensive intermixing of air strata and dilution of the airand-fibre suspension. For example, a twentyfold dilution can be achieved.

Thus, the interaction, as described above, of the two stream ensures not only the dilution of the fibrous suspension, but also intermixing of fibres which altogether improves the degree of homogeneity of the layer of fibrous material.

A detailed description of a specific embodiment of the present invention is considered hereinafter with due reference to the appended drawings, wherein:

FIG. 1 is a general view of a device for forming a layer of fibrous material of homogeneous structure; and

FIG. 2 is unit A in FIG. 1.

Referring now to the drawings, a device for forming a layer of fibrous material of homogeneous structure comprises a serrated drum 1 (FIG. 1) enclosed in a housing 2 conjugate to a vertical wind tunnel 3.

Adjacent to the serrated drum 1 is a feed table 4 with a feed roll 5 disposed thereon.

A slit-type jet nozzle 6 is installed at the place where the wind tunnel 3 adjoins the serrated drum 1. The nozzle is found directly under the drum and extends along its entire length. An upper wall 7 (FIG. 2) of the jet nozzle 6 is disposed close to the serrations 8 of the drum 1, while a lower wall 9 thereof extends above the serrations 8 of the drum 1. Thus, a channel 10 is made in between the surface of the drum 1 and the lower wall 9 of the jet nozzle, the serrations 8 of the drum 1 being inscribed in said passage. The lower wall 9 of the jet nozzle 6 adjoins the rear wall 11 of the working portion 12 of the wind tunnel 3. The wind tunnel 3 is provided with an effuser 13 (FIG. 1) incorporating a threedimensional grate l4, alsothe working portion 12 with an adjusting blading device 15 and two diffusers l6, 17 with a constant area section 18 provided there between.

Located in the bottom portion of the tunnel 3 is a metal screen 19. A packing roll 20 is installed close to the diffuser 17.

An air duct 21 is positioned in the zone of diffuser 17 under the screen 19 to connect the lower portion of the wind tunnel to an exhaust blower 22.

The device for forming a layer of fibrous material operates as follows.

In rotation, the feed roll 5 (FIG. 1) brings a layer of fibrous mass distributed on the feed table 4 towards the serrated drum 1 which is also rotating. The drum serrations, when interacting with the layer of fibrous mass, break-up the latter layer into separate fibres and groups of fibres which are taken by the serrations of the drum 1 and during rotation of the latter enter the working portion 12 of the wind tunnel 3. As a result of friction occurring between the fibrous mass and the serrations of the drum 1 at the moment of breaking upsaid mass into separate fibres and groups thereof, fibrous particles are electrically charged, positive and negative charges being simultaneously generated.

An air stream is established in the working portion of the wind tunnel and this is achieved as follows. When the exhaust blower 22 (FIG. 1) is running, outside air (shown by the arrows a") is drawnin the effuser 13. Large-size whirls established in the air entering the effuser 13 are damped by the three-dimensional grate 14 which is also serving the function of an electrostatic neutralizer for charged fibres, said neutralizer ionizing the air.

The converging walls'of the effuser 13 make the air stream narrower which is conducive to equalizing the structure of the air stream. At the same time, due to the above narrowing, the air stream is gradually accelerated to a required velocity. So, a uniform air stream is established in the efiuser, gradually increasing its velocity with the simultaneous ioninization of air.

From the effuser 13 the ionized air stream enters the working portion of the tunnel 3.

By means of the adjusting blading device 15 the velocity field profile is adjusted to achieve uniform distribution of fibrous particles across the entire area of the flow perpendicular to the screen 19. The adjustment is performed due to the effect of variable resistance provided by altering the blade spacing of the blading device 15.

In providing the ionized air stream'in the wind tunnel due to rarefaction developed by the blower 22 (FIG. 2), the jet nozzle 6 creates an air stream (as shown by the arrows b) which passes around the serrations 8 of the drum 1 to removefibres and groups of fibres off the serrations. I

The drum serrations 8 are instrumental in creating additional disturbance resulting in setting up small-size whirls in the air stream, said whirls separating grouped fibres in the outlet zone of the jet nozzle slot (as shown by the arrows c) where in a flat-shaped-air stream is formed, saturated with fibrous particles.

The flat air stream merges the ionized air stream in the wind tunnel (as shown by the arrows a) and this is accompanied by neutralization of electrostatic charges of fibres. This prevents a possibility of reversal grouping of electrically charged particles brought to life due to separating groups of fibres by the effect of a turbulent air flow developed by the jet nozzle 6.

Merfing of the air stream (as shown by the arrows c") (FIG. 2) and the air stream (as shown by the arrows a) taking place in the wind tunnel makes the stream saturated with fibrous particles several times more diluted with air. As a result, a uniform air-andfibre suspension is established in the'diffuser 16 with such a concentration which ensures practically independent motion of fibrous particles.

As the air-and-fibre suspension moves down towards the screen 19 (FIG. 1) the velocity of said suspension is reduced due to the increased cross area of the wind tunnel.

The screen 19 traps fibrous particles distributed in the air stream which results in forming on the surface of said screen a layer of fibrous material of homogeneous structure with randomly positioned fibrous particles achieved due to intermixing of air mass at merging the flat air stream and the air stream in the wind tunnel itself.

As it can be evident fromtheabove description, the device according to the present invention for forming a layer of fibrous material of homogeneous structure makes it possible to obtain a layer of fibrous material with a high degree of structural homogeneity.

A layer of fibrous material with a high degree of structural homogeneity is an efficient base for producing various kinds of materials (for example, paper, nonwoven fabric, etc.) possessing high mechanical-andphysical properties such as tear resistance, degree of porosity, resistance to snicking, soaking capacity, etc.

I claim:

1. A device for forming a layer of fibrous material of homogeneous structure, comprising a serrated drum, which breaks up fibrous mass into singular and grouped fibres; a wind tunnel, wherein an air-and-fibre suspension is established due to the introduction of singular and grouped fibres in to the air stream; a screen in said wind tunnel, with fibrous particles of air-and-fibre suslength thereof.

2. A device as claimed in claim 1, wherein the electrostatic neutralizer for charged fibres is made as a three-dimensional grate serving simultaneously for equalizing the air stream. 

1. A device for forming a layer of fibrous material of homogeneous structure, comprising a serrated drum, which breaks up fibrous mass into singular and grouped fibres; a wind tunnel, wherein an air-and-fibre suspension is established due to the introduction of singular and grouped fibres in to the air stream; a screen in said wind tunnel, with fibrous particles of air-andfibre suspension precipitating onto said screen; an electrostatic neutralizer for charged fibres, said neutralizer being located at the inlet of said wind tunnel; a slit-type jet nozzle delivering air to the zone of removing fibres from said serrated drum to separate grouped fibres and intensive intermixing thereof, said nozzle being installed at the place where said serrated drum adjoins said wind tunnel underneath said drum and along the entire length thereof.
 2. A device as claimed in claim 1, wherein the electrostatic neutralizer for charged fibres is made as a three-dimensional grate serving simultaneously for equalizing the air stream. 